The present invention relates to a safety apparatus for rotary components of an internal combustion engine, and more particularly to a throttle valve opening and closing device for controlling intake air flow rate.
Conventionally, there are throttle valve opening and closing device, in which a torsion coil spring is wound around a rotary shaft of a throttle valve. However, since the torsion coil spring requires certain length in the axial direction, the length of the rotary shaft has to be lengthened for the corresponding length to make the overall size of the device bulky. For this reason, there has been proposed a throttle valve opening and closing device which employs a spiral spring in place of the torsion coil spring (for example, Japanese Patent Application Laid Open No. 46346-1984.
However, in the throttle valve opening and closing device employing the spiral spring as set forth above, when breakage of the spiral spring occurs, the broken end can expand in diameter to hook on a hooking pin and so forth to bias the throttle valve in opening direction.
According to the present invention, it is an object to provide a throttle valve opening and closing device for an internal combustion engine which can provide enhanced safety, in which the throttle valve will never biased in the opening direction even when breakage of the spiral spring is caused.